Ligand-Controlled Mixed-Valence Copper Rectangular Grid-Type Coordination Polymers Based on Pyridylterpyridine

Six mixed-valence Cu^ICu^II compounds containing 4‘-(4-pyridyl)-2,2‘:6‘,2‘ ‘-terpyridine (L1) or 4‘-(2-pyridyl)-2,2‘:6‘,2‘ ‘-terpyridine (L2) were prepared under the hydrothermal and ambient conditions, and their crystal structures were determined by single-crystal X-ray diffraction. Selection of CuCl₂·2H₂O or Cu(CH₃COO)₂·H₂O with the L1 ligand and NH₄SCN, KI, or KBr under hydrothermal conditions afforded 1-dimensional mixed-valence Cu^ICu^II compounds [Cu₂(L1)(μ-1,1-SCN)(μ-Cl)Cl]_n (1), [Cu₂(L1)(μ-I)₂Cl]_n (2), [Cu₂(L1)(μ-Br)₂Br]_n (3), and [Cu₂(L1)(μ-1,3-SCN)₂(SCN)]_n (4), respectively. Compound 5, prepared by layering with CuSCN and L1, is a 2-dimensional bilayer structure. In compounds 1−5, the L1 ligand and X (X = Cl, Br, I, SCN) linked between monovalent and divalent copper atoms resulting in the formation of mixed-valence rectangular grid-type M₄L₄ or M₆L₆ building blocks, which were further linked by X (X = Cl, Br, I, SCN) to form 1- or 2-dimensional polymers. The sizes of M₄L₄ units in 1−4 were fine-tuned by the sizes of X linkers. Reaction of Cu(CH₃COO)₂·H₂O with L2 and NH₄SCN under hydrothermal conditions gave mixed-valence Cu^ICu^II compound [Cu₂(L2)(μ-1,3-SCN)₃]_n (6). Unlike those in 1−5, the structure of 6 was constructed from thiocyanate groups and the pendant pyridine of L2 left uncoordinated. The temperature-dependent magnetic susceptibility studies on compounds 1 and 4 showed the presence of mixed-valence electronic structure.